A clock selection circuit and synthesizer that is capable of selecting an optimum clock signal from among a plurality of clock signals in a short time. The collar comprises a body defining an interior that defines an airspace between the collar and the housing of the fluid flow sensor when the collar is positioned on the fluid flow sensor. The compartment that is currently being loaded is opened such that the pair of walls forming the compartment are spread apart, in particular, are pivoted apart, which will alter the compartment that was loaded immediately prior to it such that the product contained therein will be straightened and compacted. The reservoir has an uncompressed state and a compressed state.